(a) Field of the Invention
The present invention relates to a data transfer system capable of selecting a low-cost call type and, more particularly, to a data transfer system suited to a mobile communication system which transfers data either by a packet switched call or by a circuit switched call.
(b) Description of the Related Art
The number of users accessing the internet by using a mobile terminal, such as a cellular phone, has been remarkably increased in these years. The internet service providers offer a variety of services for e-mail, games, shopping, stock transaction and so on. Among others, the services now attracting the attention of an increasing number of users include those services for allowing e-mails or web sites to transmit or exhibit multimedia data such as including photographs and moving pictures.
The data communications performed by the cellular phone systems generally use packet switched calls. The packet switched call is considerably superior to the circuit switched call so long as only the characters, which generally have a relatively smaller amount of information, are used in the data communication. However, if the transmission data in the mobile communication system include a moving picture having a larger file size, there is a problem in that the packet switching system often involves a larger communication cost compared to the circuit switching system.
In addition, the time length needed for the transmission of a data file has been increased together with the increase of the amount of data in the data file, which raises a problem with respect to the man-machine interface. The increased time length also involves another man-machine interface problem in that the user is restricted for its operation of the mobile terminal during the increased time length for receiving the data file.
In the circumstances as described above, there are some proposals for improving the utilization efficiency of the communication links or reducing the communication cost. Patent Publication JP-A-2000-174770 describes a technique for switching the data paths in a multi-link radio communication network based on the information of the current status of the links monitored, to thereby maintain a constant communication rate irrespective of the current status of the links.
JP-A-2000-253180 describes a technique for automatically selecting one of the links in a network based on the contents to be transmitted, in order to efficiently acquire contents of the information such as multi-media data or text-base data.
JP-A-2000-307660 describes a radio data communication system for improving the utilization efficiency of the communication links by using either the packet switching communication link or the circuit switching communication link. It is described therein that the circuit switching network now used for data transmission is switched to the packet switching network for achieving continued data transmission, if it is difficult to maintain the communication using the circuit switching network or if the amount of data being transmitted by the circuit switching network is reduced.
JP-A-2001-282677 describes a data transfer system which is capable of efficiently using the resources in the system upon transferring to a mobile communication terminal a multi-media data mail including a variety of data such as audio data and/or picture data in addition to the text data. In the described technique, by transmitting transfer assist data to the mobile terminal of the mail destination by using a mail server based on the control data and allowing the multi-media data to include the control data, the mobile terminal can deliver a request of data transfer based on the transfer assist data to prevent, an unnecessary data transmission. This efficiently utilizes the memory resources in the mobile communication terminals without increasing the traffic of the mobile communication network.
JP-A-2001-320424 describes a mobile terminal which is capable of adequately selecting networks based on the types of data to be transmitted/received through the networks. This is achieved by selecting the communication paths suitable to additional data, such as audio data or picture data, based on the additional data acquired by a main data acquisition block and added to the main data, thereby achieving the data transmission at a lower communication cost.
Neither of the conventional techniques as described above, however, teach the concrete technique which enables a mobile terminal in the data transfer system to select by itself a low-cost communication link based on the type of calls while considering a variety of current statuses of the communication links as a whole.